The advent of fuel cells as alternative propulsion systems or auxiliary power units (APU's) for automotive and other similar applications, and the advent of advanced engines having capability for lower emissions and better fuel efficiency, have created a need for improved and highly specialized gas flow control valves. This includes diesel fuel reformate valves which may be used with APU fuel cells for example, or to provide Nox reductants for emissions control in advanced diesel engines, or for other uses. A reformer or fuel processor, can convert a hydrocarbon fuel (e.g., methane, propane, natural gas, gasoline, diesel, oxygenated hydrocarbons, and the like) to hydrogen or to a less complex hydrocarbon. More particularly, fuel reforming can comprise mixing a hydrocarbon fuel with air, water, and/or steam in a mixing zone of the reformer prior to entering a reforming zone of the reformer, and converting the hydrocarbon fuel into, for example, hydrogen (H2), byproducts (e.g., carbon monoxide (CO), methane (CH4), inert materials (e.g., nitrogen (N2), carbon dioxide (CO2), and water (H2O)). Also, fuel cells for example are known to use hydrogen gas as an energetic fuel for exothermic combination with oxygen at high temperature. Hydrogen may be supplied continuously to a fuel cell as a “reformate” product. At start-up of the reformer, however, the reformer operating temperature typically is too low for production of a satisfactory percentage of hydrogen in the reformate. Therefore, until the reformer achieves a sufficiently high temperature, the fuel cell is typically not started and the reformate output is diverted to a waste burner rather than being simply discharged to the atmosphere. As the percentage of hydrogen in the reformate increases, the reformate output stream is diverted away from the burner by a diverter valve and to the fuel cell. Sensitive control of such diversion is highly important to satisfactory operation of the fuel cell. Additionally, regarding emissions technology, Hydrogen reformate may need to be directed to a Diesel Particulate Filter (DPF), trap (DNT), or other device.
However, rigorous requirements must also be met by these diverter valves. The requirements of such valves, including material properties, would include capability to operate at very high temperatures and in corrosive environments with a minimum tolerance for leakage. Degradation of materials resulting from sustained exposure to such conditions can diminish valve performance significantly, leading ultimately to valve and system failure. Some components of prior art valves, such as force-balancing springs, may experience appreciable set or relaxation at high temperatures, rendering them useless. Additionally, their working lifetimes may be significantly shortened. Operating at such high temperatures can cause excessive linear expansion and failure in critical elements, rendering gas metering inaccurate or impossible.
Additionally, many valve designs are impractical for automotive applications due to excessive size, prohibitive cost, slow response, and required actuation force. The cost of some prior art valves can approach or exceed the targeted cost of the entire vehicle reformer system for which a flow-control valve is intended. For at least these reasons, prior art valves are not suitable for automotive applications for example.
What is needed is a sectional gas flow control valve assembly having valve section components which can withstand extremely high operating temperatures (for example 600°-900° C.), and having actuating section components which can operate in moderately high temperatures (for example 100°-150° C.). Thus, insulating seals and/or structures for thermally isolating the valve section components from the actuating section components are needed. It is also desirable for the valve section to be self-cleaning in order to clean debris or soot which could inhibit the actuation of the valve causing the valve to remain stuck in an open or closed position. Depending upon the application, such a valve assembly could be relatively small and lightweight, inexpensive to manufacture, highly reliable, and virtually leak-proof. A design which is also self-cleaning and thus not prone to malfunction due to being clogged with debris or soot is also desirable.